The present invention relates to surge arresters and, more particularly, to high voltage surge arresters.
Current designs of power lightning arresters used to dissipate electrical surges induced by lightning typically employ the use of a varistor block that switches with overvoltage, dissipating the excess current and clamping the voltage transient. These modules may be supported and held together by use of a ceramic/porcelain housing and springs or fiberglass structures (crimped rod or wraps) to force sufficient block contact and provide mechanical structural integrity. Larger blocks may have issues dissipating heat when discharging large amounts of energy caused by defects and excessive heating. These issues may lead to eventful failure (e.g., explosion failure of block). Block interfaces, mechanical structure and voids are known issues that are difficult to control with existing designs. As block diameter increases, the center of the block generally does not uniformly share in dissipating the energy/current or is not as utilized as the outer portion of the varistor block. An example of such a current design block is shown in FIG. 1 and described in U.S. Pat. No. 5,680,289 (“the '289 patent”).
Current varistor blocks generally become more difficult to manufacture as diameter increases for multiple reasons such as powder forming, drying and firing uniformity. The challenge of controlling these issues generally increases with diameter. An alternative approach first introduced by General Electric and subsequently licensed to other entities around the world included deploying the standard smaller blocks in parallel stacks, but employing the same previously cited structural designs, to alleviate the issues with larger block cost, availability and performance. Each of the stacks was separated from the others by air.